The present invention relates to methods and apparatus for determining the provenance of data carrying discs, such as compact discs (CD), and digital versatile discs (DVD).
The traditional CD is a read only storage medium. Originally, CDs were used for the storage of music and other audio data. However, formats, such as the CD-ROM format, have been developed facilitating the reliable storage of data for use by computers and other digital devices. The CD-ROM format has become very popular and has become the mass data storage medium for computer programs and other files.
CDs can store about 74 minutes of high quality stereo sound or about 650 megabytes of data or some combination of both. The value of a CD to the end user, because of the value of the data it stores, is typically much more than its physical cost. This has made it an attractive target for counterfeiters who can produce replicas of an original CD at a nominal cost and sell the replicas, at the market price for the data, to make large profits.
With distribution media such as audio tapes or video cassettes, the quality of counterfeit copies tends to be lower than that of the originals due to the corruption of the analogue signal in the copying process. There is no such degradation in the case of discs such as CDs, however, as all of the information is stored digitally. Counterfeiters can therefore produce counterfeit copies of CDs which are almost indistinguishable from original or bona fide CDs.
If it were possible to distinguish between an original or bona fide CD and a counterfeit, then the problems caused by counterfeiters could be substantially reduced. Law enforcement officials, for example, would have a means of identifying counterfeit CDs, and could more easily obtain search warrants and secure prosecutions. If a CD carries a program, that program could be used to check that it was loaded from a bona fide, original CD.
The present invention seeks to identify counterfeit CDs and other data carrying discs.
According to a first aspect of the present invention there is provided a method of determining the provenance of a data carrying disc, the method comprising the steps of reading uncorrected data from the disc and extracting information about errors from the data read, and comparing the error information with characteristic error information which characterises data carrying discs produced from a known source to determine whether the data carrying disc has been produced from the known source.
The manufacturing process for a data carrying disc, such as a CD, begins with the production of a master, and in the physical manufacturing process of the master, variations are introduced which give the master distinctive physical characteristics and cause errors in the data. The master is used to form generations of discs, and the physical characteristics of the master are passed on, down the generations. A group of discs manufactured from the same source, therefore, consistently exhibit the physical characteristics of the master, and those physical characteristics can be used as a xe2x80x9cfingerprintxe2x80x9d for, or identification of, that source. This invention has relevance to all data carrying discs, such as CDs and DVDs (digital versatile discs) and other optical discs, where errors in the data, which arise out of the physical manufacturing process, are consistently reproduced in all discs originating from the same source.
Thus, in a method of the invention, the error information extracted is representative of errors arising from the physical manufacturing process and acts as a fingerprint for a particular known source in the manufacturing process.
An embodiment of a method of the invention may be used to identify that a data carrying disc is genuine when the error information extracted from the disc correlates with the characteristic error information from a known and genuine source. Similarly, the absence of correlation between the error information and the characteristic error information may be used to identify a counterfeit disc.
CDs carrying popular music or computer programs, for example, may originate from a number of masters from manufacturing plants in different countries. What is more, the or each master will not be used to directly form the CDs. Each master is used in the production of a number of stampers which are used to produce the discs sold in the marketplace. It will, therefore, be appreciated that although the fingerprint of one master will be apparent in its progeny, each stage of the process will also introduce fingerprints from the sources used in those stages. It is therefore possible that if error information extracted in an embodiment of a method of the invention is compared only with characteristic error information from one genuine source there will no correlation. For example, if the characteristic error information arises from one master, but genuine CDs can have been manufactured from one of a number of masters, there may be no correlation and yet this will not necessarily mean that the disc under test is counterfeit. Accordingly, unless the characteristic error information to be used in the comparison is known to be characteristic of the single and only master, it will generally be necessary to store characteristic error information from a number of masters or other sources.
The characteristic error information with which the error information is compared may be representative of errors which have arisen during the manufacture of the known sources. Additionally, and/or alternatively, the sources from which discs are produced may be impressed with characteristic error information to provide copy protect signals to signify that a disc is from a genuine source.
The characteristic error information, with which the extracted error information is compared, may be read from a disc whose provenance is known, for example, in real time as the error information is extracted. A correlation may then be made between the extracted error information and the characteristic error information from the known and genuine disc in order to determine the likelihood that the disc under test is a counterfeit.
In a preferred embodiment, characteristic error information is obtained from a group of discs from a common source, for example, which are all known to have been produced from a common and genuine master, or a common and genuine stamper. Error information common to each of the discs in the group is then extracted and stored to provide the characteristic error information with which the error information from a disc under test is compared.
Methods of the invention may be used, as described, to determine whether a disc is genuine or counterfeit. Alternatively, the method may be used to establish the degree of similarity between a disc under test and discs from a known source.
When data carrying discs such as CDs and DVDs are read, the digital data is processed to correct errors so that the normal output is error free.
The error correcting process is undertaken in various stages. Thus, where the disc is read by a laser, a bit stream is formed which is then, for example, divided into blocks, which blocks are translated into bytes and then into frames, the frames being subjected to error correction and then being assembled into sectors and encoded. The encoded data is then divided into sub-channels.
In a method of the invention, the uncorrected information read from the data carrying disc may be taken from any of the stages or levels of data which are produced. The method requires that the data which is read reveals errors which have arisen from the physical manufacturing process. Thus, the data which is read has not generally undergone significant error correction.
Alternatively, the normal reading process may be modified to extract uncorrected information from the data carrying disc.
Clearly, appropriate processing means may be used to enable data at any stage or level to be read and error information to be extracted.
In a reader for a CD or DVD, for example, there are drive means to position the laser relative to sectors on the disc and the positioning data used by such drive means is not error free. Furthermore, readers already incorporate means to read this positioning data. In a preferred embodiment of a method of the invention, it is proposed to extract the error information from positioning data read from the data carrying disc.
Where the disc is a CD, it is preferred that a method of the invention reads the Q-subchannel blocks of data in order to enable the extraction of the error information.
In an embodiment of a method of the invention particularly relevant to present day CDs and their readers, the method further comprises the steps of reading the Q-subchannel blocks of a CD and determining which Q-subchannel blocks have been corrupted or are missing, and comparing the list of corrupted or missing blocks with a characteristic list of corrupted or missing blocks.
The characteristic list of corrupted or missing blocks may have been produced by reading a group of CDs from a common source, determining for each disc a list of corrupted or missing blocks, and then forming a characteristic list of corrupted or missing blocks common to all of the CDs of said group.
In an embodiment, a number of characteristic lists obtained from groups of genuine CDs are stored and the error information extracted from a disc under test is compared with all of the characteristic lists whereby it is determined if the CD is genuine.
The present invention also extends to apparatus for enabling the provenance of a data carrying disc to be determined, said apparatus comprising a disc reader for reading uncorrected data from a data carrying disc, and processing means for extracting information about errors from the data read, and for comparing the error information with characteristic error information which characterises data carrying discs produced from a known source to determine whether the read data carrying disc has been produced from the known source.
In an embodiment, said apparatus comprises means for identifying that a data carrying disc is genuine when the error information extracted from the disc correlates with the characteristic error information from a known and genuine source.
In an embodiment, said apparatus comprises means for storing characteristic error information from a number of known sources.
Additionally and/or alternatively, said apparatus may comprise means for storing characteristic error information which has been impressed on known sources.
The processing means may be arranged to compare the extracted error information with characteristic error information read from a disc whose provenance is known as the error information is extracted.
According to a further aspect of the present invention there is provided apparatus for enabling the provenance of a data carrying disc to be determined, said apparatus comprising a disc reader for reading blocks of data from a data carrying disc, processing means for identifying and listing blocks of the data which have been corrupted or are missing, storage means for storing a characteristic list of corrupted or missing data blocks which characterises discs produced from a known source, and means for comparing the identified list with the characteristic list to determine if said disc has been produced from said known source.
Preferably, the disc reader is arranged to read blocks of positioning data such that blocks of positioning data which have been corrupted or are missing can be listed and compared with a characteristic list of corrupted or missing positioning data blocks.
In an embodiment, where the disc is a CD, said disc reader is preferably arranged to read the Q-subchannel blocks in order to extract the error information.
In an embodiment, the processing means is arranged to determine which Q-subchannel blocks have been corrupted or are missing, and to compare the list of corrupted or missing blocks with said characteristic list of corrupted or missing blocks.
The characteristic list of corrupted or missing blocks may have been produced by reading a group of CDs from a common source, determining for each disc a list of corrupted or missing blocks, and then forming a characteristic list of corrupted or missing blocks common to all of the CDs of said group.
In an embodiment, said apparatus has storage means for storing a number of characteristic lists obtained from groups of genuine discs, and said processing means is arranged to compare the identified list with all of the characteristic lists whereby it is determined if a disc under test is genuine.
The methods and apparatus defined above enable genuine and counterfeit discs to be distinguished where, for example, all genuine discs come from a common source such that they all carry the unique fingerprint of that common source. However, where there is more than one genuine source for a group of discs, unless the tester has access to characteristic error information, or fingerprints, from all genuine sources, the determination of the provenance of a test disc can be left in some doubt. Thus, the result of a test might be that this disc is likely to be counterfeit because it does not correlate with the finger print information stored.
Thus, it may be preferred to impress a characteristic fingerprint or unique identifying error information on to all genuine discs when they are made.
According to a still further aspect of the present invention there is provided a method of incorporating identifying error information into a data carrying disc, where the data carrying disc is physically manufactured either directly or indirectly from a master, and wherein the master is produced by a manufacturing process which is controlled by processing means, the method comprising the step of providing identifying error data to said processing means such that said identifying error information is incorporated in the master during its formation.
Thus, all manufacturing plants for proprietary audio material or software could be provided with unique identifying error information for that material which identifying error information is impressed into the master, and hence into any copies made therefrom, during manufacture. Methods and apparatus of the invention for determining the provenance of the discs can thereby reliably identify all genuine discs, and hence all counterfeits.
Methods and apparatus of the invention can be used not only to identify genuine or counterfeit discs, but also to deny access to the data on counterfeit discs.